Pressure and temperature-dependent gauche-trans isomerization of 1-bromopropane: Raman measurement and statistical thermodynamic analysis

Raman measurements of the isomerization equilibrium in liquid 1-bromopropan e are compared with perturbed hard-body fluid predictions. The integrated a reas of the Raman bands arising from the C-Br stretch of the gauche and tra ns conformations are used to track the isomerization equilibrium as a funct ion of pressure and temperature. Repulsive solvent-solute interactions are treated using the recently developed excluded-volume-anisotropy model (base d on realistic molecular structures for the two isomers and the equation of state of liquid 1-bromopropane), and cohesive interactions are treated usi ng the van der Waals mean field approximation. The results illustrate the d elicate balance of attractive and repulsive solute-solvent interactions whi ch underlie the effects of solvation on chemical equilibria. Comparison of the measured and predicted changes in Delta H with pressure, and Delta V wi th temperature, are used to determine parameters describing the attractive mean field and cavity formation energies of the two isomers, as well as the isomerization enthalpy and entropy of the isolated molecule. (C) 1999 Amer ican Institute of Physics. [S0021-9606(99)00705-9].